1. Field of the Invention
The present invention relates to a servo control apparatus, and, in particular, to a servo control apparatus which performs servo control of operation of a to-be-controlled object using software.
2. Description of the Related Art
There is a recording-medium reproducing apparatus in which a recording medium such as a magnetic tape is driven and information recorded in the recording medium is read.
Such an apparatus may have a pitch-control function for adjusting an information reading speed as a result of controlling a recording-medium feeding speed. Such an apparatus may perform the pitch control using hardware, specifically, using an analog circuit, or may perform the pitch control using software, specifically, using a microcomputer.
When the pitch control is performed in an analog manner by using discrete circuits, an IC, or an LSI circuit, a clock signal which is changed in accordance with a desired information reading speed is directly provided to such a circuit(s). On the other hand, when the pitch control is performed by using software, a clock of a fixed frequency is connected to a particular microcomputer, a special circuit detects data for the pitch control, and execution of the software is controlled so as to respond to the detected data, and, thus, the pitch control is achieved.
FIG. 1 shows a block diagram of one example of an information storing apparatus in the related art.
The information storage apparatus 100 stores digital sound information in a magnetic tape cassette for 8-mm VTR. The information storage apparatus 100 mainly includes a mechanical portion 101, a servo microcomputer 102, a system microcomputer 103, a signal processing block 104, a clock-signal generating portion 105, an ATF circuit 106, an A-D/D-A converting portion 107, and a key operating portion 108.
In the mechanical portion 101, the tape cassette 110 containing a magnetic tape 109 is loaded, and the magnetic tape 109 is wound on a rotation drum 112 in which magnetic heads 111 are fixed.
The rotation drum 112 is rotated by a drum motor 113. The magnetic tape 109 is sandwiched by a capstan motor 114 and a capstan roller 115, and is caused to run at a predetermined speed as a result of the capstan motor 114 rotating. As a result, the magnetic tape 109 slides on the magnetic head 111 at a relative speed. Thus, a signal is read from tracks, which are formed on the magnetic tape 109 in a manner in which the tracks are inclined with respect to the tape running direction.
The thus-read signal is supplied to the signal processing block 104. The signal processing block 104 demodulates the read signal and outputs the demodulated signal through the A-D/D-A converting portion 107. Further, the signal processing block 104 generates a SERVO ref signal for controlling the rotation phase of the rotation drum 112 and provides the SERVO ref signal to the servo microcomputer 102. The servo microcomputer 102 is connected with the drum motor 113, the capstan motor 114 and so forth, and performs servo control of the rotation of the rotation drum 112 and the running speed of the magnetic tape 109 so that the relative speed between the magnetic head 111 and the magnetic tape 109 is fixed.
A fixed-frequency clock 116 is connected to the servo microcomputer 102, and the servo microcomputer 102 operates using a clock signal provided by the fixed-frequency clock 116. The servo microcomputer 102 performs the servo control through execution of a previously set software.
The system microcomputer 103 is connected to the servo microcomputer 102, and the servo microcomputer 102 performs the servo control in accordance with commands and pitch data provided by the system microcomputer 103. The key operating portion 108 is connected to the system microcomputer 103, and the commands and pitch data are recognized by the system microcomputer 103 in response to key operation in the key operating portion 108, operation of the system microcomputer 103 itself and operation of other external equipment. Then, the system microcomputer 103 provides the thus-recognized commands and pitch data to the servo microcomputer 102 and the clock-signal generating portion 105. The system microcomputer 103 operates using a clock signal provided by a fixed-frequency clock 117.
The clock-signal generating portion 105 has fixed-frequency clocks 118 and 119, generates various clock signals, and provides the clock signals to the signal processing block 104, ATF circuit 106 and A-D/D-A converting portion 107. The ATF circuit 106 operates using the predetermined clock signal generated by the clock-signal generating portion 105, detects an ATF error signal from a reproduced signal, and provides the detected ATF error signal to the servo microcomputer 102.
The servo microcomputer 102 performs the servo control in accordance with the commands and ATF error signal. Also, at the time of pitch-control reproduction, the servo microcomputer 102 performs reproduction at a speed in accordance with the pitch data provided by the system microcomputer 103.
FIG. 2 shows a flowchart of operation of the servo microcomputer 102.
The servo microcomputer 102 is initialized by start of power supply or the like (in a step S6-1). Then, in response to the commands, which are provided by the system microcomputer 103 in response to an operation of a reproduction key in the key operating portion 108, the servo microcomputer 102 starts control of the mechanical portion 101 through drum servo, capstan servo and so forth (in a step S6-2). Thus, the servo microcomputer 102 enters a reproduction condition.
In the reproduction condition, the servo microcomputer 102 performs a drum servo routine (a step S6-3), a capstan servo routine (a step S6-4), and a reel servo routine (a step S6-5) in sequence.
In the drum servo routine (the step S6-3), the capstan servo routine (the step S6-4), and the reel servo routine (the step S6-5), the pitch data which is provided by the system microcomputer 103 in accordance with the pitch data input through a key operation in the key operating portion 108 is processed through execution of software, and the servo control is performed.
In the drum servo routine (the step S6-3), the pitch data is recognized (in steps S6-31, S6-32). In the step S6-31, when the pitch data is 0%, that is, when the reproduction speed is not changed, a drum servo parameter for determining a reference condition for the drum servo control is set to a previously set reference value, and the drum servo control is performed (in steps S6-33, S6-34).
When the pitch data provided by the system microcomputer 103 has a positive value in the step S6-32, that is, when the reproduction speed is increased, the drum servo parameter is set to the value obtained as a result of the absolute value of the pitch data value being added to the previously set reference value, and the drum servo control is performed (in a step S35 and the step S34).
When the pitch data provided by the system microcomputer 103 has a negative value in the step S6-32, that is, when the reproduction speed is decreased, the drum servo parameter is set to the value obtained as a result of the absolute value of the pitch data value being subtracted from the previously set reference value, and the drum servo control is performed (in a step S36 and the step S34).
In the capstan servo routine (the step S6-4), the pitch data is recognized (in steps S6-41, S6-42).
In the step S6-41, when the pitch data is 0%, that is, when the reproduction speed is not changed, a capstan servo parameter for determining a reference condition for the capstan servo control is set to a previously set reference value, and the capstan servo control is performed (in a steps S6-43, S6-44).
When the pitch data provided by the system microcomputer 103 has a positive value in the step S6-42, that is, when the reproduction speed is increased, the capstan servo parameter is set to the value obtained as a result of the absolute value of the pitch data value being added to the previously set reference value, and the capstan servo control is performed (in a step S6-45 and the step S6-44).
When the pitch data provided by the system microcomputer 103 has a negative value in the step S6-42, that is, when the reproduction speed is decreased, the capstan servo parameter is set to the value obtained as a result of the absolute value of the pitch data value being subtracted from the previously set reference value, and the capstan servo control is performed (in a step S6-46 and the step S6-44).
In the reel servo routine (the step S6-5), the pitch data is recognized (in steps S6-51, S6-52).
In the step S6-51, when the pitch data is 0%, that is, when the reproduction speed is not changed, a reel servo parameter for determining a reference condition for reel servo control is set to a previously set reference value, and the reel servo control is performed (in steps S6-53, S6-54).
When the pitch data provided by the system microcomputer 103 has a positive value in a step S6-52, that is, when the reproduction speed is increased, the reel servo parameter is set to the value obtained as a result of the absolute value of the pitch data value being added to the previously set reference value, and the reel servo control is performed (in a step S6-55 and the step S6-54).
When the pitch data provided by the system microcomputer 103 has a negative value in the step S6-52, that is, when the reproduction speed is decreased, the reel servo parameter is set to the value obtained as a result of the absolute value of the pitch data value being subtracted from the previously set reference value, and the reel servo control is performed (in a step S6-56 and the step S6-54).
Thus, in each of the drum servo routine (the step S6-3), the capstan servo routine (the step S6-4) and the reel servo routine (the step S6-5), a process for causing the servo parameter to reflect the pitch data, input through key operation in the key operating portion 108, is executed through execution of software.
Thus, in the servo microcomputer 102, the pitch control operation in accordance with the input pitch data is performed through the execution of the software. Therefore, because the steps for processing of the pitch data should be executed, a response of the pitch control in response to the input of the pitch data is slow, and operation performance of the pitch control is not good.
Further, because the servo microcomputer 102 performs the servo control based on the pitch data, the software is complicated. Furthermore, since the control operation is started after the pitch data is detected, a time lag occurs, and it is difficult for the pitch data to be smoothly followed.